There is enormous pressure on health care providers to continue practicing the most expensive medicine in the world. To resist that pressure, we need some help from policymakers.

Consider the case of a man I'll call Mr. A. At the age of 80, he is admitted to intensive care after a huge stroke. He also has pneumonia and kidney failure. He is too sick to tell us his views on aggressive care at the end of life, but his family is happy to fill the void. They insist we use every tool at our disposal to prolong his life, despite brain scans making it clear that he will never again be able to walk, talk or feed himself. The total bill for the last month of life? Many tens of thousands of dollars.

Or contemplate Mrs. B's case. She arrives at the ER with shortness of breath. Tests find iron deficiency anemia. The most likely cause, based on her history, is an ulcer — probably a benign one. We can perform an upper GI X-ray, do a blood test for a bacterial infection that commonly causes ulcers and send her home with pills. Or we can opt for more precise, and far more expensive, tests in which a specialist examines her innards with a fiber-optic scope and takes tissue samples. In rare cases, this procedure catches something an X-ray can't. When presented with the options, the patient chooses the scope. The result? She spends an unnecessary night in the hospital, has $1,000 or more of tests and goes home with the same diagnosis and the same medicines she would have if we'd done the far less expensive X-ray.

Both of these patients are composites of people we see at the hospital every day, and they demonstrate why it will be so hard to rein in health care spending. Americans have spent the last several decades hearing that all you have to do is be a little assertive to get top-of-the-line treatment. They have had prescription coverage through their health insurance for so long that they have trouble understanding why I won't prescribe a convenient Z-Pack of antibiotics (at a cost of $60 or so) instead of amoxicillin, which they have to remember to take three times a day (at a cost of about $4). Websites and magazines tell them that if the doctors say a condition is untreatable, they should shop around for a specialist.

Health care rationing is already in place, of course, for uninsured people. If they qualify for care in public systems like the one in Houston's Harris County, where I live, it takes weeks to get through the administrative process and longer still to get an appointment at a clinic. And if a patient needs a specialist, that will mean another wait, which can lead to life-threatening delays in diagnosis and treatment. Medicaid (and soon Medicare) patients also face rationing of a sort, in that they often can't find doctors willing to treat them.

Paradoxically, even as costs are rising, hospitals and doctors are finding their work to be less and less profitable. Even the best insurance plan won't cover the entire cost of Mr. A's hospital stay, and Mrs. B's HMO may deny coverage for even a one-night hospital stay. Doctors who accept patients admitted from the ER are often working for free or paid a small subsidy by the hospital, and those who see uninsured or Medicaid patients are unlikely to recoup enough to cover their overhead.

Some efforts are being made to control costs. Hospitals keep an eye on "unnecessary days," and medical personnel are becoming experts on "cost-effective care." But the savings of such efforts are insignificant compared with what we spend on futile care at the end of life, or expensive tests and treatments that lead to better outcomes in only a tiny fraction of cases.

Even though President Barack Obama's health care plan will expand the number of people with insurance, it won't change the reality that we cannot afford to give every patient and family all they want, or to provide four-star medicine when the three-star version is almost as likely to succeed.